Others have made gear lubricants having low ratios of Brookfield viscosity to kinematic viscosity at 100° C. using polyalphaolefins, or combinations of petroleum derived base oils with significant levels of viscosity index improver. For example, Chevron Tegra® Synthetic Gear Lubricant SAE 80W-140 is made with highly refined petroleum derived Group III base oil and greater than 20 wt % viscosity index improver. Chevron Tegra® Synthetic Gear Lubricant SAE 75W-90 is made with polyalphaolefin and diester base oils. Tegra®°is a registered trademark of Chevron Corporation. Polyalphaolefin base oils are expensive and have less desired elastomer compatibility than other base oils. Diester base oil provides improved elastomer compatibility and additive solubility, but is also very expensive and available in limited quantities.
European Patent Application No. 1570035A2 teaches that functional fluids may be made using base oils having low CCS viscosity, wherein the functional fluids also have low Brookfield viscosity. Nothing is taught regarding selection of base oils having more a desired molecular composition or low traction coefficients.
Commonly assigned U.S. Patent Application Publication No. 20050133407 discloses that gear lubricants may be made having a low Brookfield viscosity from a Fischer-Tropsch derived lubricating base oil having a desired molecular composition. Commonly assigned U.S. patent application Ser. No. 11/296,636, filed Dec. 7, 2005, discloses that base oils with high VI and having low aromatics and preferred high levels of predominantly molecules with monocycloparaffinic functionality can be used to blend manual transmission fluids with very high VIs and low Brookfield viscosities at −40° C. Commonly assigned U.S. Patent Application Publication Nos. 20050258078, 20050261145, 20050261146, and 20050261147 disclose that blends of base oils made from highly paraffinic wax with Group II or Group III base oils will have very low Brookfield viscosities. Commonly assigned U.S. Patent Application Publication No. 20050241990 discloses that wormgear lubricants may be made using base oils having a low traction coefficient made from a waxy feed. Commonly assigned U.S. Patent Application Publication No. 20050098476 discloses pour point depressing base oil blending components made by hydroisomerization dewaxing a waxy feed and selection of a heavy distillation bottoms product. Commonly assigned U.S. Provisional Patent Application 60/599,665, filed Aug. 5, 2004 and U.S. patent application Ser. No. 10/949,779, filed Sep. 23, 2004, discloses that multigrade engine oil blends of Fischer-Tropsch derived distillate products and a pour point depressing base oil blending component prepared from an isomerized bottoms product may be made having low Brookfield viscosities.
A gear lubricant is desired having a higher kinematic viscosity at 100° C. and lower Brookfield Ratio than the gear lubricants previously made. Preferably, the gear lubricant will have a kinematic viscosity greater than 10 cSt at 100° C., and will also have a low Brookfield viscosity relative to kinematic viscosity; and a process to make it is also desired. Preferably, the gear lubricant will also not require high amounts of viscosity index improver.
A lubricant base oil having a very low traction coefficient, and finished lubricants including gear lubricants made from the base oil, are also highly desired.